Pulse repeating system



Jan 1945. R SHANCK 2,366,836

PULSE REPEATING} SYSTEM Filed July 10, 1943 FIG/ mm mm m man CALL/N6 f vo FIG. '2

ANSWERING SWITCH HOOK FLASHES FROM CALLED END FIG. 3

FROM CALLED END 3 M g e lNl/L'NTOR RB. SHANCK BVW v A TTORNEV Patented Jan. 9, .1945

Roy B. Shanck, Douglas Manor, N. Y., assignor to M Bell. Ielephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 10, 1943, Serial No. 494,208 IllClaims. (01. 179-84) The invention relates to pulse repeating systems and more particularly to systems of this type operating on a duplex basis.

tis an object of the invention to provide a pulse repeating system with a simplified duplex balance and capable of eflicientoperation under conditions of line variations and interference.

It is a more specific object of the invention to provide a system of this type which with standardized. equipment is adapted for repeating selecting and supervising pulsesrfor telephone switching systems over lines of greatly differing characteristicsand lengths. i v

The selective and supervisory operations of automatic telephone switching-systems are frequently performed. over extensive line circuits, such as toll lines, the lengths of which differ greatly and which are subject -to. well-known disturbances and. interferences. The selecting pulses, usually termedthe dial pulses, are usually transmitted from one telephone exchange .to another over half-duplex pulse repeating circuits, which hitherto. have been carefullybalanced to operate satisfactorily under the changing oper- -ating conditions in the lin circuit. The reason for duplexing the pulse circuit is mainly to. be.

found in the fact that :the trafli-c requirements include the transmission in both directions over ance is perfect. For this purpose the polar relay may be connected in any well-known manner,

as by having its operating windings directly included in the two balanced branches or connected in abridge between the balanced circults, in accordance with well-known practices in telegraph repeating systems. The system is also equipped for the transmission of busy signals comprising a series of pulses of a predetermined frequency, usually about 80 cycles per minute, which are impressed upon the duplex circuit by operation of the pol changer. it V As is well known it has hitherto beennecessary to establish -a fair balance between th line circuit and the balancing network induplex systems of either type referred to above, inorder to "prevent th receiving relay from responding to the outgoing pulses. Whensignals are impressed on an unbalanced system. unbalance currents arise which may operate the receiving relay. Thus in the difierential duplex .circuitthe :currents in the two operatingwindings will be unequal or unbalanced and the stronger current may. operate the relay., In the bridge duplex circuit the potentials applied to the. relay'winding are unequal and an'equalizingl or unbalance current will flow through the windings and may operate the relay, a

the line circuit of supervisory signals or pulses.

'The 'operations are complicated by the requirement that, in the series of operations involved in the setting up of a connection, the line circuit isplaced under two different conditions, which may be termed th idle and the busy conditions.

The pulse repeating system is adapted to receive dialing pulses from acalling station, which i may be a remote telephone subscribers station or a local operators dialing circuit, and to repeat thepulses over an outgoing line circuit to a distant telephone exchange, equipped for au- "tomatic switching in response to the dial pulses other subscribcrs station.

The repeating circuit includesja pol changing. relayfor applying two different transmitting potentials to the line circuit corresponding to the two conditions: of the pulses, namely, marking and spacing or current and'no current.

', 'Ihe pulses from the pole changing relay are; impressed upon a duplexcircuit includin'gthe line circuitin one branch-and abalaricingcircum in the other branch. l

A polar receiving relay is includedin the duplex circuit for reception of "signals incoming over th line circuit, this relay being unaffected by outgoing signals .when the impedance bal- 40 for 'the selection of another exchange or an- In accordance'with a. feature of the invention,'the balancing network is simplified and is V standardized tosupply a fair balance for a large variety of line circuits so that it maybe manufactured at comparativelylow cost. In accordance with the invention the s stem is further more arranged s thatit will be unnecessary to adjust the balancing network to compensat ror sporadic variations inthe line circuits during ordinary operating conditions including temperature and leakage changes. Thissimplification of the balancingnetwork is further effective in reducing the large amount of designing work involved in the provision of a large variety of differently dimensioned balancingnetworks for the corresponding varieties of lin circuits, to

satisfy the present day severe demands for accuracy. i

For the purposes just outlined the invention provides an arrangement for preventing false operations, which would be due to improper responses by the receiving relay. during the transmission of outgoing pulses resulting from unbalance conditions. Bythisj provision a. given design of balancing network may be. basedlon certain; average or predominant line conditions .1 among the large variety of conditions met with in the plant. Such a networkQjm-ayflthus provide an accurate balance for a large number of lines with averag characteristics; it would, however, be less accurate in the balancing of line circuits having more diverging characteristics, without, however, establishing a circuit condition which'would result in false operations due to unbalanc conditions caused by line variations' or,interfe'rence. I l

When the pulse-repeating systemis idle, the pole changing or sending relay will apply an idle condition to the toll line, which may be assumed to be a spacing or no current condition, the other end of the line circuit being assumed to apply a similar condition to the line." In response to the seizure of the repeater station by a calling station or an operator, the pole changer applies a busy or marking condition to the toll line. After the transmission of dialing pulses, the dis- .tant station also applies a marking or answering condition to the line circuit, which consequently will operate the polar receiving relay at the repeating station. l

After this condition has been reached, further pulses may be transmitted in either direction over the line circuit. For example, a rering pulse maybe transmitted by the sending, station in the form of a pulsewhich will cause the distant exchangeto rering the calledline; busy flashes maybe transmitted back to the calling line; and switchhook flashes may be transmitted in either direction.

. I The polarj receiving relay at the repeater stationwill respond to, incoming .pulses from the line circuit, and willrespond to the answering condi- .tion imposed upon the line circuit from-the distantend by operating to marking position. Thus, the receiving relay is arranged to control circuit equipmentwhich, in a Well-known manner, may

In view of the application of different line potentials under different operating conditions the act of connecting a capacitance fiiunt circuit across the relay windings may under certain circumstances cause kick-01f. Therefore, in accordance with another specific feature of the invention, provision is made for charging the capacitance shunt in alternate directions, while it is "disconnected from theline circuit, to produce a properly directed discharge current and prevent kick-off when the capacitance is connected to the line circuit during the sending of pulses.

In accordance with a more specific feature of the invention, the direction of charging current is controlled by the position of the receiving relay scription reference will be made to the attached drawing in which:

be arranged to respond in proper sequence to the.

traffic signals, such'as answering and busy, from the called line. It may furthermore be arranged to function response to dial pulses from thedistant station, when the call is in the oppotion of telephone switches ,at the'exchange with which the repeater is immediately'associated.

It will, therefore, be seen'that'ina sense the repeater operates under full-duplex conditions,

inasmuch as it will operate withv either, of two' polarities applied to either or both ends of the line circuit. However, though the repeater is required to operate in both directions, it will operate only in one direction at a time, sothat for any particular line condition the repeater will be operating on a half-duplex basis.

This particularv condition permits the introduction of a feature of the invention which basically resides in renderingthe receiving-relay ineffective during the transmission of outgoing signals and restoring the receiving relay circuit to effectiveness upon termination of theretransmission of outgoing signals.

In accordance with a more specific feature of 'windings of the receiving relay only during the sending conditionsQBy this provision any un-' balance current from the line and balancing i circuits, due tothe outgoing pulses, will be diverted from the windings of the receiving relay venting kick-off." j

.topass over the capacitance shunt, thereby presite direction, for controlof the selecting opera- 1 Figs. :1, 2 and 3 are diagrammatic .representations of different typical [pulses that may ,be,

transmitted in either direction over the line circuit; and h I Fig. 4 is a circuit diagram or a repeater circuit, representing a: specificapplication of the invention and including the features of the invention.

Referring to the drawing, it will be assumed that a subscriber's station is connected to a telephone exchange and desiresto make a call to a distant subscriber's station at another telephone 1 exchange.

tions in the telephone plant, the subscriber first removes -'his:receiver from the hook, thereby establishing a calling condition. Thereafter the subscriber operates'his calling dial which transmits the usual groups of dialing pulses. The distant exchange then applies an answering condition to the line circuitfand rings the called subsubscriber disconnecting prematurely, a rering pulse may be transmitted'from the calling end of the line circuit. flashes may be direction.

Subscribers? switchhook transmitted at any time in either t- The diagram in Fig. l shows the signaling current in theline circuit'at the .tir'ne'of a call. Thus,

when the line circuitjis seized,'the line current increases from a no current or spacing condition to a steady marking current condition. Thereafter the marking current interrupted by the dialing pulses, whereupon the line current remains steady. In th case of a subsequent rering the line current is momentarily interrupted.

Fig. 2 refers tothe conditions at the called end of the toll line,. which normally. applying a 'spacing'condition to the line circuit. Upon answering, the called exchange :transmits-a, steady line current whichmay subsequently be inter j rupted"by'switchhookflashes.

Fig; 3 shows conditions'at the called exchange when a 'busy condition exists, in ,zwhich case the The two exchanges are con nectedtogether over toll lines.

Inaccordance=-with established trafiiccondi tion in accordance with the balance between the line circuit TL and the network BN.

ingwinding onrelay 450111 a direction to keep steady marking condition isfinterrupted by spacing conditions. Referring now particularly to Fig. 4, the circuit is that of a repeater station R connected over a toll line circuit TL to a distant exchange station represented at E. l The repeater station may be assumed to be located at an exchange to which a plurality of subscribers are connected, one of which is shown at S.

The subscriber station S may bea conventional station with a switchhook SH and dial D. The station is connected over a subscribers line SL to the repeater station. However, for the purposes of the invention the line circuit SL may be connected to a toll operators circuit instead of to a subscribers station, in. which case the switchhook may be replaced by a key andthe dial by an operators pulse sending device.

The repeater station R comprises the pole changer or sending relay 400 connected in the line circuit SL to receive pulses and having contacts for alternately applying ground and battery to the line circuit TL in sending the pulses outgoing from the exchange. A source of busy signal 4H1 may be connected through busy key MI orany automatic means for applying the busy signal to the line circuit SL for operation of relay400. The pulse circuit SL through relay 400 extends over a key 420 andthrough relays430 and 440 to battery, the other end of. the circuit being connectedto ground at the dial, D.

The polar receiving relay 450 has a biasing in sending outgoing pulses will not ordinarily affect relay 450, since proportionate currents pass through the two windings in opposing rela The distant exchange E may include a suitable responsive switch control circuit AM. The station E may also include a repeater circuit similar to the circuit R with areceiving relay similar to relay 450 and with transmitting contacts 490 similar to those of relay 1400.

When the circuit is in the condition shown in the drawing, ground is applied to both ends of the line TL and to the balancing network BN so that no current will be flowing. When relay 400 operates, battery is connected to the bridge point Pandcurrent flows through onewinding over the line circuit to ground at E and through the other winding through the balancing network to ground. The windings being opposed under this biasing winding and operate relay 450 to marking. If now relay (the operated to also apply: f battery to the duplex circuit, practically no cur- -rent will flow in the line and through the upper operating winding; the battery at relay'400 will.

however, send current through the lower operatnetwork BN. Thus, the operation of relay 400 relay 450 operated to marking. Thus in receiving incoming, marking, and spacing pulses-the two operating windings of relay 450 will be in cooperative relation to operate the relay to marking or spacing, respectively.

Although the receiving relay 450 is shown in the drawing and is described herein as being connected in a difierential duplex circuit, it

should be understood that in accordance with] the invention, this relay may be connected in a duplex bridge circuit with similar advantages.

Relay 450 in marking condition applies ground to relay 460 and at the same time to a circuit equipment 410 which is part of the exchange equipment and serves in part to selectively control switches for setting up a connection in response to pulses incoming from a distant exchange to the repeater R. l i l l i A condenser C is normally connected over contacts of relays 440 and 460 to battery and ground and thus willbe normally charged in a predetermined direction. When relay 4 50 operates to marking, thereby operating relay 460, the

ground and. battery connections are reversed to the c ndenser, thereby reversing the charge on the condenser. Thus, the condenser is charged in a direction depending on the position. of relay Relay 43B is slow to attract and relay'MO is slow to release. These two relays serve to connect condenser C to the duplex circuit and todisconnect it therefrom under control of the dial pulses. With the condenser C connected to the duplex circuit, it will'provide a shunt path for the operating windings of relay 450 with 'respectto currents incoming over the line TL to the network The operation ofthe circuit will now be described. It will be assumed that the circuit is in rest condition, as shown in the drawing.

When the subscriber removes the receiver from the hook SH, ground is extended over the subscribers line SL, through the windings ofrelays 400, 430 and 440 and relays 400 and Mill quickly operateprelay 430 being slow to operate will opcrate shortly after. Relay 40B applies battery to the duplex circuit and over the line to the distant exchange E for operation of the switch control circuit 49L charging battery and connected it temporarily over the contacts of relay 430 to the duplex circuit with its battery side connected to the network RN and its grounded side to the line TL. The disfcharge currentfrom condenser Cthrough the windings of relay 450, at the moment it is connected to the duplex circuit, will thus be in a direction to aid, the biasing winding and will tend tohold the relay in spacing. Shortly thereafter the condenser C will be disconnected from the line circuit by the delayed operation of relay43fl circuit with the same polarity, thereby holding relay 450 to spacing. When the armature of relay illo reaches the grounded contact, the currents Relay 440 disconnected condenser C from the in the line and the network will be reduced to zero without affecting relay 450.

At the end of the first dial pulse relay 4'00 operates to apply battery to the duplex circuit; relay 43!] remains retracted; and'relay 440 remains attracted. During each pulse series relay 400 will repeat each marking and spacing transition, relay 430 will remain released and relay 440 will remain attracted, thereby keeping condenser C connected to the duplex circuit. During an interval between pulse series relay 46!] remains attracted, relay 440 also remains attracted and relay 430 may or may not be attracted depending upon the durationof the interval. During the succeeding series of pulses these operations are repeated.

Thereafter steady battery will be applied to the duplex circuit by relay 408 inmarking condition and relays 430 and 440 will remain attracted, thereby disconnecting condenser C from the duplex circuit, and causing it to be recharged.

-When the answering condition is established at the distant end of the line TL, as by the contacts 490 operating to battery, relay 450 will op erate to marking, thereby applying ground to the circuit equipment 410 for the proper reception of the answering signal. Relay 450 also operates relay 460 to reverse the battery connection to 0011- some-composite arrangement.

It will now be assumed that some special circumstance arises, as for example, that thedistant .subscriber hangs up prematurely, necessitating the sending of further pulses from the calling end, for example, a rering pulse, as indicated in Fig. 1. Therelay 400 would momentarily interrupt the battery connection to the line. Relay .430 would quickly release and relay 440 would remain attracted. Thus, during the. sending of the grounded pulse over the line circuit the condenser C will be bridged across the windings of relay 450 with a reversed polarity, and the discharge current through the operating windings of relay 450 will hold the relay to marking. The condenser furthermore provides a by-path for unbalance currents asjalready described. vAt the end of the pulse, relays 400, ltiland 440 would all remain attracted, thereby disconnecting the condenser from the line circuit and recharging it.

In the case a busy condition existed at the distant end after all dial pulses were transmitted, a series of pulses, shown in Fig. 3, would be transmitted by the contacts 690 over the line TL, through the windings of relay 456 and network BN to ground, causing relay 450 to operate in unison with the busy pulses and apply, corresponding busy pulses to the circuit 410 for suitable response. The consequent operation of relay 460 will cause the condenser to be charged in opposite directions but will ultimately leave the condenser charged in the direction which corresponds to the final position of. relay 450.

In the case of a call incoming to repeater station R, relay 450 would be operated tomarking'in response-to the application of battery at the dis- ,tant exchange E to thelinei Subsequent interruptions, as by dial pulses, would cause relay 450 to oscillate and apply corresponding pulses to the circuit'dlll for selective operation of switches. In response to this selective operation a switch may ultimatelyconnect the subscribers station S to the repeater station R. This switch is diagrammatically represented by contacts LF; contacts LF may also represent a line finder switch for connecting the subscriber, station to the repeater in response to a call by the subscriber. With the subscriber connectedin this manner, switchhook flashes maybe transmitted back to the station E in the manner already described.

In case thesubscriber S is busy, the connection at switch LF will remain open and the cir- -cuit 410 may be arranged to automatically operate the key 4H for application of busy signal from interrupter 4H1. Relay 400 will operate in unison with the busy pulses and relays 430 and 44B will-produce corresponding holding impulses for relay 450 and establish the by-path for the windings of relay 450, as already described.

On observing the busy signal, the distant calling station at E will hang up and thus will send a disconnect signal by applying steady ground over contacts 490, through the windings of relay 450, thereby operating the relay to spacing. The circuit 4.10 respondingto thisoperation may be arranged to automatically disconnect the inter.- rupter 410 by means of contacts 4| l, whereupon the whole system will be restored to idle condition.

The relays 430' and 440 may, by means of the key 420, be connected directly to the apex P of the duplex circuit. In operated position the key 420 completes the su-bscribers line SL through relay 40!] directly to battery. Under this condition relays .430 and 440 will not be operated directly by. the subscribers dial D but will be operated in response to the corresponding opera;- tions by relay 490. The operations of the entire system will be the same as already. described with the difference that those of relays 430 and 440 .will be slightly delayed with respect to the operations of relay 400 as compared with conditions described above. l

It should be understood that the key 420 may be omitted and the circuit connected permanently in eitherofthe two manners provided by-the key. j

The inductance I is inserted between the contacts of relay 400 andthe apex P for the purpose of shaping the outgoing pulses in any desired manner. v

The purpose of connecting condenser C across the duplex circuit is attainedduring transmission of outgoing ,pulses. Thus, in accordance with the invention and as already explained above, the balancing. network is of simple construction and is designed so that networks of this kind.

may be used universally with tolllines of different lengths and different characteristics. It is, of course, within the scope of the invention that a few standardized types of network may .be provided, eachtype to be used with lines having characteristics within comparatively narrow limits and the different types of network supplementing one another to satisfy the require c n and mftqu se vi e, as subject to sporadio yariatio'ns in their characteristics a which arebeyond control. Wherea veryclose balance is necessary, it has been the practice to continuously observe the line conditions and pcorre-k spondingly vary th balance by the network.

With the by-path condenser C connected across the operating windings of the receiving relay durings'ending of pulsesappreciable leeway is afforded in thebalancing of, the circuit, thereby permitting the use of universal networks for approximate" balancingover wide ranges and also in special cases obviating the need for continual readjustment of the network. Thus, during sending of pulses any unbalance currents that would tend to fiow in or out of the line circuit orthe network due to unbalance conditions would find a low impedance path through the condenser C and thus would avoid the higher impedance path through the two operating windings in series of relay 450.

By always charging the by-pathcondenser in a direction correspondingto the position of the receiving relay, it is insured that this relay will not be operated when the by-path is closed.

It should be understood that the invention may readily be adapted for application to a telegraph repeating system with similar advantages, where sending takes place against two different signaling conditions imposed by the remote station.

What is claimed is: LA two-way signaling system comprising an approximately balanced line circuit normally maintained alternately in marking and spacing steady state conditions, receiving relay means at one end of said line circuit having contacts for coming marking and spacing signal pulses superimposed on said steady state conditions, auxiliary circuit means including relay means connected to be responsive to-outgoin marking and spacing signal pulses to prevent said control by said contacts in response to unbalance currents due capacitance means,"and said switching means comprises circuit means for preconditioning sald capacitance means for connection into said shunt path without production of false impulses under either of said alternative steady state conditions of said line circuit.

4. A two-Way signaling system in accordance with claim 1 in which said auxiliary circuit means further includes a desensitizing circuit for said receiving relay means, slow-acting relay' means 'for connecting said 'desensitizing circuit to said receiving relay means in response to outgoing marking pulses of predetermined length, and other slow-acting relay means for disconnecting said desensitizing circuit irom said receiving relaymeans in response to an outgoing marking pulse longer than said predetermined length.

5. A two-way signaling system comprising a line circuit normally maintained alternately at steady marking and spacing potential applied at the distant end, a signal repeatingcircuit connected to the other end of said line circuit and comprising a balancing circuit for approximate impedance balance against said line circuit, receiving relaymeans connected in duplex relation to said line and balancingcircuits and having control contacts, sending contact means connected for passing outgoing signals into said line andwbalancing circuits, a receiving circuit connected for control by said control contacts, auxiliary circuit means responsive to outgoing signals for preventing false operation of said. receiving controLof a receiving circuit in response to inrelay means in response to unbalance currents between said line and balancing circuits during transmission of outgoing signals, and switching means connected for preconditioning of said auxiliary circuit means in accordance with said ceiving circuit in accordance with marking and spacing pulses of signals incoming over said line circuit and superimposed on said steady state conditions, sending contact means connected for passing outgoing signals into said line and balancing circuits, auxiliary circuit means con nected to be responsive to marking and spacing pulses of the outgoing signals to prevent said control by said relay means contacts in response to unbalance currents between said line and balancing circuits produced by operation of said rents for the conditioning of said auxiliary circuit means for the proper prevention of said control underboth of said steady state condiv tions.

3. A two-way signaling system in accordance with claim 1 in whichsaid auxiliary circuit means further includes a, shunt path for the winding sending contact means, and switching means connected to'be responsive to incoming line curalternate marking and spacing conditions to prevent false operation of said receiving relay means by said auxiliary circuit means.

6. A signaling system in accordance with claim 5 in which said auxiliary circuit means includes a capacitance circuit and timed relay means responsive to outgoing signal transitions for connecting said capacitance circuit between said line and balancing circuits for by-passing unbalance currents due to said transitions.

'7. A signaling system in accordance with claim 5 in which said auxiliary circuit means includes a capacitance shunt for said receiving relay means and timed relay means responsive to outgoing signal transitions for completingsaid shunt during sending, and said switching means includes a current source and is responsive to said receiving relay means for precharging said capacitance means from said source alternately in opposite directions in accordance with said steady marking and spa'cing potentials. a r

8. In a balanced duplex signaling circuit, a receiving relay, a capacitance shunt path for said relay, circuit means responsive to outgoing pulses for connecting said shunt to said relay for by passing unbalance currents during sending and r including a charging circuit for saidcapacitance shunt path to precondition said path for connection to said relay without operating said relay.

9. In a balanced duplex signaling circuit adapted for sending against alternate line conditions of marking and spacing potentials, a receiving relay responsive to said conditions and having operating windings, a normally open capacitance shunt path for said relay, a charging circuit for said capacitance shunt path,.timed circuit means responsive to outgoing signal pulses for connectcircuit of said receiving relay means including a for precharging. and switching means responsive to said receiving relay means to reverse the direction of precharging for locking of said receiving relay means in its prevailing position by the; discharge current when said shunt path is connected across'said windings.

10. A two-way signaling circuit for transmission in both directions one at a time which comprises ,a line having a near end, a balancing circuit, receiving relay means connected to said near end of theline and to said balancing circuit and having control contacts for control of. a receiving, circuit in response to'incoming line ourrents-,. sending contact means connected, for passing outgoing signalpulses into said. line and said balancing circuit, auxiliary circuit means including relay means connected to be. responsive. to

outgoing signal pulses for preventing said control by said control contact means in response to unbalance currents due to said outgoing pulses,

reversing contact means connected to a remote point on said line for normally applying, alter.- nately marking and spacing steady state conditions to said line, and switching means. connected to be responsive to incoming line currents for conditioning of said auxiliary circuit meansvfor the effective prevention of said control by said control contacts under both of said steady state conditions. i ROY B. SHANCK, 

